European Patent Publication 0 392 783 (Coleman et al.) describes efforts to obtain azlactone graft copolymers via functionalization of a poly-alpha-olefin base polymer by grafting a monomeric 2-alkenyl azlactone using reactive extrusion processing. Compatibilized blends and blends with base polymer are also disclosed.
Many desirable and useful graft copolymers result from this method. But there is an upper temperature limit of about 200.degree. C. in the grafting process because monomeric 2-alkenyl azlactones are volatile. The reactive extrusion temperature range limits the types of base polymer candidates for reactive extrusion. For example, nylon 6 and certain polyurethanes are not suitable candidates for reactive extrusion according to the method of Coleman et al.
Another difficulty with graft copolymers prepared by reactive extrusion is the uncertainty of products and byproducts of the reactive extrusion process. Uncertain products can include degraded or crosslinked base polymer, homopolymer of the graft comonomer, and uncertain grafting configurations on the desired graft copolymer product. The presence of unreacted monomer is deleterious to performance of the resulting product, particularly when the resulting product is used for an article prepared by injection molding. Also, depending on the type of free radical initiator employed in the reactive extrusion process, crosslinking of thermoplastic polymer can occur that would otherwise deleteriously affect use of the graft copolymer for further processing.
One purpose of preparing azlactone-functional graft copolymers is to provide azlactone-functional surfaces for subsequent reaction with nucleophilic groups, including biologically active substances. One method of providing azlactone-functional surfaces is to functionalize pre-existing surfaces of an article. But such methods are limited by the complexity of the process and the ability of the treatment to affect such pre-existing surfaces.
An example of chemical treatment of a pre-existing surface to impart functionality is disclosed in Edelman et al., Proc. Nat. Acad. Sci. USA 68, 2153 (1971), which describes how to functionalize nylon monofilament fibers using 3N HCl to partially hydrolyze the fibers before protein could be coupled using a water-soluble carbodiimide. Partial hydrolysis can weaken the physical properties of the polymer, such as strength, flexibility, resiliency to stretching, etc.
An English language abstract of Japanese Kokai 92,159 published by the American Chemical Society discloses the use of azlactones as compatibilizers in a blend of nylon and polycarbonate polymers.
U.S. Pat. No. 4,695,608 (Engler et al.) discloses the bulk polymerization of vinyl monomers and alkenyl azlactones using free radical polymerization techniques.